We will continue a detailed analysis of the growth requirements of various normal human and mouse cells and their transformed counterparts. During the coming year, particular emphasis will be given to the following: 1) Characterization of a small peptide growth factor that is produced by several types of transformed cells and stimulates their growth at clonal density; 2) identification of factors from serum protein that are needed for clonal growth of normal and transformed human fibroblasts in the best currently available media; 3) detailed analysis of the growth requirements of human epidermal keratinocytes, which we can now culture without a feeder layer or conditioned medium. The long-term goals of this study are: 1) To understand fully the growth requirements of various types of normal cells from humans and from animals used in cancer research, 2) to understand the changes in growth requirements and growth regulation that occur in malignancy, and 3) to identify differences between normal and malignant cells of potential value in future clinical treatment of malignancy.